1. Technical Field
The present invention relates to a system for measuring dynamic, unsteady pressures within a fluid or medium, including a fluid or medium having an extremely high temperature such as steam, flowing inside a pipe and using it to determine a parameter (e.g., flow velocity and/or speed of sound) of the fluid or medium; and more particularly to a system for measuring the same using a piezoelectric-based sensor device or the like.
2. Description of Related Art
Techniques are known that enable flow and fluid parameter measurements which utilize an array of strain-based sensors, clamped onto the outside of a process piping. Depending on the specifics of the application, it is often desirable to use a strain sensor design to measure the circumferentially averaged strain within a pipe. One method to achieve circumferentially averaged strain within a conduit utilizes strain sensitive piezoelectric strips or bands. Although the flow monitoring systems designed with piezoelectric material as the sensing element have proven to be effective, application of such a system is often severely limited by the maximum operating temperature for the piezoelectric material, which limits applications for use in relation to pipes having an extremely high temperature fluid or medium such as steam.
For example, PVDF sensors used for a known flow meter product are limited to relatively low-to-medium temperature applications, with the current upper temperature limit or rating of about 125° C. This limit is derived from the material operating limits, due to the requirement that the sensors be in contact with the pipe to measure the pipe strain caused by pressure variations in the fluid traveling through the pipe. In the chemical industry in particular, the 125° C. temperature limit is quite restrictive as many processes will run over this limit. It is believed that with some development, higher temperatures on the order of 150° C. may be possible, but even with such temperatures, the maximum operating temperature of PVDF-based sensing materials is far short of a significant amount of the process temperatures for a significant amount of flow metering applications that are needed.